1. Field of the Invention
The present invention relates to an aluminum alloy for forging which is used for automobile parts, electronic appliances, etc., and which exhibits a tensile strength of at 10 least 30 kgf/mm.sup.2 and an elongation of at least 15% after forging and subsequent T.sub.6 -treatment.
2. Description of the Related Art
As a typical material for forging of aluminum alloy, 6061 alloy has been used. Since 6061 alloy is used as a forging material after extrusion, the forging material becomes costly. Moreover, since extruded 6061 alloy is forged, the shapes of the products of the alloy are naturally restricted to simple ones.
Accordingly, the material for forging is required to be prepared by casting when a product having a complicated shape is to be produced. JIS cites AC4C, AC4CH, etc., as materials which can be forged when they have been cast to have a predetermined shape, that is, when they are used as preformed ones. However, aluminum alloys such as AC4C and AC4CH exhibit poor tensile characteristics such as elongation, compared with 6061 alloy, and, therefore, forged products excellent in shape characteristics cannot be obtained therefrom.
Japanese Unexamined Patent Publication (Kokai) No. 54-13407 discloses that to increase the elongation of an aluminum alloy material for forging obtained by casting an aluminum alloy such as AC4C and AC4CH, the eutectic Si is refined by decreasing the Si content to as small as about 3% by weight and adding Na, Sr, Sb, etc.
Although the elongation can be improved to some extent by refining eutectic Si, the elongation of the resultant alloy is still unsatisfactory compared with that of 6061 alloy. As a result, there still remain problems with regard to the forgeability. Moreover, since the forged products thus obtained have an insufficient yield point, they are required to have a thick wall for the purpose of giving them a predetermined structure strength. As a result, the advantages of aluminum materials as lightweight parts cannot be currently utilized.
In view of the current situation as described above, the present inventors have disclosed an aluminum alloy the properties of which are improved by refining eutectic Si in Japanese Unexamined Patent Publication (Kokai) No. 5-9637.